As pointed out in U.S. Pat. No. 4,970,340, trialkyl amine oxides can be made by reacting a trialkyl amine with aqueous hydrogen peroxide. They are useful for many purposes such as hair conditioners in shampoos as described in U.S. Pat. No. 3,086,943. When a C.sub.10-16 alkyl dimethyl or ethyl alkyl amine oxide as described in U.S. Pat No. 3,086,943 is made, the product will gel if the concentration of the amine oxide exceeds about 30 weight percent. This results in a fairly dilute aqueous tert-amine oxide solution. When such solutions are shipped to remote locations as they usually are, the freight charges will be fairly high because of the large amount of water that is being shipped.
Alkyl dimethylamine oxides are described in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed. At page 266, Kirk-Othmer states that "when a strictly aqueous system is employed, final concentrations of amine oxide should be limited to below 35% since higher concentrations tend to gel and prevent good mixing."
Hoh et al., J. Am. Oil Chem. Soc., 40 (1963) page 268-271 describe the synthesis of dimethyl dodecylamine oxide by reaction of dimethyl dodecylamine with 35% aqueous hydrogen peroxide. The product is a 30-40 weight percent aqueous solution of the amine oxide. Hoh et al. note that even using 35% aqueous hydrogen peroxide, the reaction mixture will gel unless diluted with water during the reaction.
Hoh et al. attempted to make dimethyl dodecylamine oxide without co-feeding water starting with 35%, 70% and 90% aqueous hydrogen peroxide. With 35% and 70% hydrogen peroxide, the product was a gel that could not be stirred. The reaction with 90% hydrogen peroxide was not completed because of darkening of the reaction mixture.
Chadwick U.S. Pat. No. 3,215,741 describes the preparation of di-C.sub.1-2 alkyl C.sub.10-20 alkyl amine oxides by reaction of the tert-amine with hydrogen peroxide. While attempting to make the desirable concentrated solutions of the amine oxide, Chadwick found that when commercially available hydrogen peroxide containing 20-90 weight percent H.sub.2 O.sub.2 was used, the reaction sets up to a gel resembling a thick starch paste long before completion of the reaction. Chadwick's solution to the problem was to co-feed at least 20% hydrogen peroxide and sufficient water to the tert-amine such that the final product was water diluted. When dimethyl dodecylamine was used the most concentrated amine oxide solution that could be obtained was only 30-40 weight percent amine oxide.
Other disclosures in which relatively dilute aqueous solutions of tertiary amine oxides are formed include U.S. Pat. No. 4,247,480 wherein carbon dioxide is used as a reaction promoter, and EP 307 184 A2 published Mar. 15, 1989 wherein low temperature reactions in the presence of carbon dioxide are carried out in order to minimize nitrosamine formation in the product.
U.S. Pat. Nos. 4,970,340, 5,130,488, and 5,208,374, and JP 51/32505, published Mar. 19, 1976, describe processes in which concentrated aqueous solutions of tertiary amine oxides are formed via oxidation of specified tertiary amines with hydrogen peroxide.
U.S. Pat. No. 4,748,275 describes the discovery that solid non-hygroscopic flakeable di-C.sub.14-30 alkyl C.sub.1-2 alkylamine oxide is made by reacting di-C.sub.14-30 alkyl C.sub.1-2 alkylamine with aqueous hydrogen peroxide containing at least 40 weight percent H.sub.2 O.sub.2 in the absence of a solvent. The solid product is recovered by crystallization at low temperature or by vacuum stripping of the solvent from the reaction product.
U.S. Pat. No. 5,075,501 describes non-hygroscopic solid tertiary amine oxide dihydrates useful in the preparation of dry detergent formulation such as laundry powders. These products are made by oxidizing certain mixed tertiary amines with aqueous hydrogen peroxide having a concentration of 50-90% by weight at 20-100.degree. C. in the presence, at least during the latter part of the reaction, of an organic solvent in which the tertiary amine and the tertiary amine oxide are soluble at the reaction temperature but in which the tertiary amine oxide is insoluble at a lower temperature. In a comparative example it is shown in the patent that when no organic solvent (ethyl acetate) was used the reaction mixture formed a paste which cannot be fluidized even by increasing the temperature.
It would be of advantage if a way could be found for producing solid tertiary amine oxide products having two methyl and/or ethyl groups and one long chain primary aliphatic hydrocarbyl group without need for use of organic solvents, water dilution, low temperature crystallization procedures, or vacuum distillation operations. This invention is deemed to fulfill this objective in a highly efficient manner.